JavaScript -- 基础点

数据类型的判断

// 1 判断数据具体是哪个类的实例 (构造器)
    var str = 'abc'
    var num = 123
    var boo = true
    var arr = [1, 2, 3] 
    var obj = {
    
    }
    var fun = function() {
    
    }
    var nul = null
    var und;

    console.log(Object.prototype.toString.call(str))  // '[object String]' 
    console.log(Object.prototype.toString.call(num))  // '[object Number]' 
    console.log(Object.prototype.toString.call(boo))  // '[object Boolean]' 
    console.log(Object.prototype.toString.call(arr))  // '[object Array]' 
    console.log(Object.prototype.toString.call(obj))  // '[object Object]' 
    console.log(Object.prototype.toString.call(fun))  // '[object Function]' 
    console.log(Object.prototype.toString.call(nul))  // '[object Null]' 
    console.log(Object.prototype.toString.call(und))  // '[object Undefined]'